SYNOS is a very difficult space shooter, but not all the difficulty lies where you'd want it
Similar to games like Geometry Wars, you goal is simply to survive the onslaught for as long as possible. Every 2 minutes you stay alive, you get 1 point, the object being to get up to 9. Well, sadly I never lived past 3 minutes myself, despite many attempts. The biggest problem with the game is that there's too much happening on the screen and you'll easily loose track of your fighter. This is due not only to tons of enemies and super-colorful gunfire which draws the eye, but also because as you play, the background scene changes, in some cases to colors that are just hard to look at. It's all very bright, but its rather too much, and you'll likely get hit by a stray bullet when you're looking elsewhere for your ship.
80 MS points ($1 US) isn't a whole lot, and so you may give it a shot just to see since the price is so low. However, with plenty of other great $1 games on XBL (Shoot 1UP or Miner Dig Deep) there's not a huge incentive to buy it, unless you're plain bored with your other games.